Photographic media containing an improved amine enhancer system

ABSTRACT

In a photographic medium containing a furfurylidene, an aromatic amine enhancer system and a lower haloalkane sensitizer, the use of an improved amine enhancer system consisting of a mixture of at least one aromatic amine and a polyhalo-substituted phenylenediamine results in improved heat and light stability, and greater shelf life.

United States Patent [72] Inventors John Alan Mattor Hollis; Lawrence Price, Old Orchard Beach, both of Maine [21 Appl. No. 746,254

[22] Filed July 22, 1968 [45] Patented Oct. 26, 1971 [73] Assignee The Scott Paper Company Delaware County, Pa.

Continuation-impart of application Ser. No. 641,720, Apr. 21, 1967, Pat. No. 3,394,395 Continuation-impart of application Ser. No. 626,720, Mar. 29, 1967, Pat. No. 3,394,393, Continuation-impart of application Ser. No. 351,316, Mar. 12, 1964, now abandoned.

[54] PHOTOGRAPHIC MEDIA CONTAINING AN IMPROVED AMINE ENI-IANCER SYSTEM 9 Claims, No Drawings [52] US. Cl

Primary ExaminerNorman G. Torchin Assistant Examiner.lohn Winkelman Att0rneys.lohn A. Weygandt, William J. Foley, John W.

Kane, .Ir., Stanton T. Hadley and Martin L. Faigus ABSTRACT: In a photographic medium containing a furfury- I lidene, an aromatic amine enhancer system and a lower haloalkane sensitizer, the use of an improved amine enhancer system consisting of a mixture of at least one aromatic amine and a polyhaIo-substituted phenylenediamine results in improved heat and light stability, and greater shelf life.

PI-IOTOGRAPIIIC MEDIA CONTAINING AN IMPROVED AMINE ENIIANCER SYSTEM RELATED APPLICATIONS This application is a continuation-in-part of U.S. Ser. No. 641,720 filed Apr. 21, 1967, now US. Pat. No. 3,394,395 issued July 23, 1968 for PHOTOSENSITIVE MEDIUM COM- PRISING A FURFURYLIDENE, A PRIMARY AROMATIC AMlNE AND A LOWER l-IALOALKANE, and of U.S. Ser. No. 626,720 filed Mar. 29, 1967, now US. Pat. No. 3,394,393 issued July 23, 1968 for PHOTOGRAPHIC MEDIUMS BASED ON FURFURYLIDENES WITH l-CHLORO-2,4- PHENYLENEDIAMINE ENHANCER. The two parent applications were in turn both continuations-in-part of US. Ser. No. 351,316 filed Mar. 12, 1964, now abandoned. The subject matter of the present application is related to the subject mater of U.S. Pat. Nos. 3,394,391; 3,394,392 and 3,394,394, all issued July 23, 1968 and 3,413,121, issued Nov. 26, 1968.

BACKGROUND OF THE INVENTION The parent applications describe a photographic medium comprised of a furfurylidene derivative, a primary aromatic amine enhancer and a lower haloalkane sensitizer. The primary aromatic amine enhancer is described as a primary aromatic amine preferably containing two primary amino groups each of which is in resonance with a benzene ring and more preferably, these amino groups are positioned meta to each other on the same benzene ring. The amines are further characterized as having up to two other functional groups on the ring but preferably only one, with a functional group adjacent an amino group. Specific amine compounds include 2,6dichloro-p-phenylenediamine, 2-chloro-p-phenylenediamine, p-hydroxy-aniline, m-phenylenediamine, 4- halo-m-phenylenediamines, 4-methoxy-m-phenylenediamine, 2,4-toluenediamine, 4-ethyl-m-phenylenediamine, benzidine, 3,3'-dimethoxy benzidine, 4-phenoxy-m-phenylenediamine, 4,4dianilines, etc., with the m-phenylenediamine, monosubstituted-m-phenylenediamines, 2,4-toluenediamine, 4,4'-dianilines and benzidines giving the best results. Priorto the present invention 4-chloro-m-phenylenediamine was the most desirable amine, producing a photographic medium which when applied to the flexible substrate has a shelf life at room temperature of about 6 weeks.

Shelf life of a photographic film or medium is very important as long periods of time often elapse between the production of the film and its use. It has been discovered that after about 6 weeks the photographic media containing the 4- chloro-m-phenylenediamine become prematurely activated causing discoloration of the photographic medium. The photographic media containing other described primary aromatic amines become prematurely activated in less than 6 weeks; therefore, the other primary aromatic amines described are even less desirable than the 4-chloro-m-phenylenediamine. While the film bearing the photographic medium which has become prematurely activated can be imaged, developed and fixed, the imaging characteristics are altered unpredictably and the background areas remain permanently discolored. Thus the premature activation of the photographic medium is highly undesirable. Unique combinations of aromatic amine enhancers have been discovered which when substituted for the primary aromatic amine enhancers of the previously described systems result in photographic mediums presently having demonstrated 6 month shelf lives without background discoloration.

In addition, photographic media containing the new aromatic amine enhancer system of the present invention produce images which exhibit greater stability to light and to heat than the images produced by photographic media containing the previously described primary aromatic amines. In view of the fact that, following exposure, the image is developed and the background fixed by heating the photographic medium, the importance of a heat stable image is readily apparent. Images produced by the photographic media containing the previously described primary aromatic amine enhancers are somewhat heat degradable and care must be exercised during the development and fixing process to insure that the temperature employed is high enough to develop the image but not so high as to degrade the developed image while the background is being fixed.

The developed images produced by the photographic media containing the amine enhancer system of the present invention are substantially more light stable than the images produced by the photographic media containing the previously described aromatic amine enhancers. The images produced by the previously described media degrade, becoming lighter and more brown upon exposure to light. The photographic media embodying the present invention exhibit little lightening or browning after prolonged exposure to light.

It is a further advantage of the present invention that photographic media prepared with polyphenylene oxide as the resinous binder and containing the new aromatic amine enhancer system produce images having unique optical densities. When this new amine enhancer system is employed in conjunction with polyphenylene oxide resin binders the images generally go from the colorless background to their maximum optical density in from four to seven steps on a Stauffer 2l-Step Wedge. The photographic media containing the previously described primary aromatic amines in polyphenylene oxide resins generally require at least l2and usually more steps to go from background to maximum optical density. Stated in another manner, the present invention results in images of greater maximum, or of the same optical density produced by a smaller exposure than required by the previously described systems. This is important not only because less exposure is required to produce maximum optical density but the range of exposure giving maximum optical density is increased.

The photographic media of the invention produce images which are black, gray or dark brown over the entire exposure range. In the past those enhancers most acceptable in respect to shelf life tended to produce images more brownish than black. Moreover, the tendency in many cases has been for the image to vary in hue depending upon the degree of exposure. It has been possible to produce black images in such cases by adding an auxiliary enhancer to the mono-substituted enhancer generally employed, but previously used auxiliaries have invariably undesirably shortened the shelf life of the finished product. The present invention not only produces good and stable blacks, but at the same time actually increases the shelf life of the product over that of a comparable product from which the poIyhalo-substituted phenylenediamine compound has been omitted.

Other advantages of the present invention will readily become apparent.

DESCRIPTION OF THE INVENTION The present invention is directed to a new and improved aromatic amine enhancer system to be employed in production of photographic media. More particularly, the present invention is directed to a new aromatic amine enhancer system to be employed in conjunction with a furfurylidene derivative color former and a lower haloalkane sensitizer.

As previously indicated, the basic photographic medium, improved by the substitution of the new aromatic amine enhancer system of the present invention of the previously described primary aromatic amines, is described in U.S. Pat. Nos. 3,394,391; 3,394,392; 3,394,393; 3,394,394; 3,394,395 and 3,413,121. The teachings of these patents are incorporated by reference.

The photographic medium of the present invention consists essentially of a furfurylidene derivative as the color-forming ingredient, an aromatic amine enhancer system and a lower haloalkane sensitizer. The photographic medium is negative working an is usually carried as a film on an impervious flexible support.

In the present specification and claims, the term furfurylidene derivative refers to color-forming furfurylidene compounds and preferably furfurylidene derivatives corresponding to one of the formulae wherein nis 1 or 2, with X, when nis 1, being a hydroxyl, 1 amino, phenyl, or naphthyl radical, and when nis 2 being absent or a phenylene, naphthylene or 4,4'-biphenylylene radical; and X is a methyl, nitro, or furfurylidene imine radical or a carbon atom forming a part of a cyclic acetal ring with the other x to give a difurfurylidene pentaerythritol.

The furfurylidene derivative is prepared in accordance with known procedures by reacting furfural with, for example, an amine or polyol. The reaction product is purified, and admixed with a solvent and the other ingredients of the photographic medium to prepare a coating solution. The coating solution is applied to a suitable support such as coated paper and dried to leave the photographic medium in the form of a film which upon drying becomes photosensitive. A print is made by exposing the film through a photographic negative to light, followed by heating of the exposed film to a temperature greater than 100 C. to develop the image.

Preferably the sensitizer employed in the photographic medium is a solid at room temperature having a purity of at least 98 percent with compounds containing one to two carbon atoms being preferred. Representative preferred compounds are iodoform and pentabromoethane. Iodoform is preferred. However, carbon tetrabromide and pentabromoethane have been satisfactorily employed.

The aromatic amine enhancer system of the present invention is a mixture containing at least one member of the group' of primary aromatic amines consisting of mor p-phenylenediamines, mono-or di-substituted mor p-phenylenediamines, aniline, N-phenyl-p-phenylenediamine, 4,4'-methylenedianiline, 4,4'-thiodianiline, benzidines or substituted benzidines and at least one member of the group of polyhalosubstituted phenylenediamines corresponding to the formula NH: NH:

wherein: in the present specification and claims, R represents bromine, chlorine, methyl, ethyl or isopropyl, R represents bromine or hydrogen and X represents bromine or chlorine. It IS critical and essential to the present invention, that when one member of the mixture is 2,6-dibromo-p-phenylenediamine or it must be employed in conjunction with at least one other member selected from either group but said other member, if only one other member employed, is not to be either 2,6- dibromo-p-phenylenediamine or 2-bromo-6-cloro-p-phenylenediamine. The 2,6-dibromo-p-phenylenediamine and 2- 6 bromo- 6-chloro-p-phenylenediamine are unique in that they are the only compounds which can be employed as a member of either group. However, as previously stated they must be employed in conjunction with at least one other member of either group as the desired increased shelf life, image stability and unique image optic optical density are not obtained unless employed in such a mixture.

In a preferred embodiment, the terms monoor di-substituted mor p-phenylenediamines refer to monohalo-mor p-phenylenediamines, dichlorophenylenediamines, monohalo-monoethyl-phenylenediamines, mono-halo-monoethylphenylenediamines, methoxy-phenylenediamines, or ethoxyphenylenediamines and the term substituted benzidines refers to 3,3 -dimethoxy or 3,3-diethoxybenzidines.

Representative polyhalo-substituted phenylenediamines included in the second group, at least one member of which is employed in combination with at least one member of which is employed in combination with at least one member the other group of primary aromatic amines include 4,6-dibromo- 1,3phenylenediamine, 2,4,6-tribromo-1,3-phenylenediamine, 3,5-dibromo-2,4-diaminoisopropylbenzene, 3,5-dibromo-2,4- diaminochlorobenzene, 2-bromo-6-chloro-l ,4-phenylenediamine, 3,5-dibromo-2,4-diaminoethylbenzene and 2,6- dibromo-l,4-phenylenediamine. The preferred polyhalo-substituted phenylenediamines are the trisubstituted diamines corresponding to the formula NH: The photographic media employing these preferred polyhalosubstituted phenylenediamines in admixture with one or more of the primary aromatic amines product images having unusual stability and optical density.

In producing the unique aromatic amine enhancer system of the present invention the primary aromatic amines or mixtures thereof comprise from about 5 to 60 percent by weight with the polyhalo-substituted phenylenediamine or mixtures thereof making up the complementary portion of the amine enhancer system, i.e. from about 95 to 40 percent by weight. In general the stability of the image and the optical density of the image increase as the proportion of polyhalo-substituted phenylenediamine is increased.

In the preparation of photographic films and other photosensitive products, the furfurylidene color-former, the amine enhancer system and the haloalkane sensitizer are dissolved in solvent solution along with a film-forming plastic polymer to form a coating composition which is applied to a suitable support material. Upon drying, the coating compositions become photosensitive. Any one of several suitable organic solvents that are volatile at room temperature or at slightly elevated temperatures such as chloroform; benzene; l,l,2trichloroethane and methyl-ethyl ketone can be employed as a solvent for the binder and photographic medium. Mixtures of the solvents can be used to obtain improved solvation. The film-forming plastic should be essentially nonreactive with the other ingredients of the solution and desirably by itself forms a translucent or transparent film that is colorless or substantially colorless so as not to interfere with or mask the color produced by the other ingredients in the photographic medium. Some polyester polymers have been found to be unsatisfactory presumably because the hydrogen halide attacks the ester linkage. The hydrogen halide is believed to be an important intermediate in the chemistry of the dye-formation reactions. Polymers containing large amounts of hydroxyl groups will usually interfere with image formation. The polymer should be unaffected by anhydrous hydrogen iodide at F. In most cases it is desirable for the polymer to form a nontacky film. Polymer film-formers or binders that are suitable for use in photographic media of the present invention include polystyrene and polyphenylene oxide.

The weight ratio of primary amine enhancer to the furfurylidene color-former is usually in the range of 0.] to l0, preferably 0.5 to 1.5. The weight ratio of haloalkane sensitizer to color-former is in the range of 0.1 to 20, preferably 0.5 to 2. The weight ratio of resin to color-former is not too important. It will usually be in the range of 1 to 40 with the lower ratios below about 5 being preferred from the standpoint of intensity. The coating solids used will normally be in the range of 10 to 20 weight percent.

A photographic plate or film is prepared from the coating solution by applying it to a suitable support by a conventional means. The coating weight applied (dry basis) will normally be in the range of 2 to 7 pounds per ream (25X38-500) to give a film thickness in the range of 0.05 to 0.5 mils. The thicker the film, the more intense the image; however, if the film is too thick, it is difficult to fix the background. The film thickness desired will be dependent upon the vapor pressures of the amines employed and the particular resin employed.

The support used in the preparation of a photographic product can have a suitable coated surface to withstand the penetration of organic solvents. in the case of paper; starch, potassium polyacrylate resins, polyvinyl alcohol, and similar binders are employed to produce the barrier coat. In general, film-forming water-soluble resins can also be employed to produce the barrier coat; however, casein and other proteinaceous resins have been found to be detrimental to the photographic medium when said resins are employed in the barrier coat. in the case of transparent supports, films of polyethylene terephthalate resin (duPont'SMylar) have proved to be excellent supports and particularly suitable for the preparation of films for microphotographic copying. Materials such as cellophane are not usable except under spe- .cial conditions because of the plasticizer present. Uncoated thin paper sheets, such as a carbonizing paper, can also be impregnated with the solutions to give a translucent appearing product or sheet.

EXAMPLES The following examples illustrate the desirable photographic characteristics exhibited by photographic media containing the amine enhancer system of the present invention: (These examples are merely illustrative and are not deemed to be limiting.)

EXAMPLE 1 A web of bleached paper bodystock having a basis weight of 45 pounds per ream (25X38inches -500) was basecoated with pounds per ream of a coating composition containing, by dry weight, 12 parts of ammonia-cut casein, 14 parts of precipitated calcium carbonate, 86 parts of a No. 1 quality domestic paper-coating clay, 8 parts of a styrene-butadiene latex, i part of tetrasodiumpyrophosphate as a dispersant, and k part of potassium oleate as a release agent, with sufficient water to bring the total solids to 50 percent.

This coating composition was applied to one side of a web of the above-described bodystock by means of an air-knife coater, and finished in sequence by means of a conventional cast-coating drum.

The resultant coated paper had a basis weight of 60 pounds per ream and an extremely smooth surface. To provide a continuous film for proper solvent holdup an intermediate coating composition was prepared, comprised of 41 parts (wet weight) of an aqueous solution containing 10 percent by weight of a potassium salt of polyacrylic acids (Modical VE sold by Nopco Chemical Company), 0.5 part of a wetting agent (Victowet 358 sold by Victor Chemical Company) and 41 parts of water to make a 5 percent solids solution. Four pounds per ream, dry weight of this coating composition was,

applied by means ofan air knife coater to the basecoated web. This coating was finished in sequence by conventional cast coating techniques in the same manner as the basecoating.

The smooth, photographically desirable coated surface thus obtained was topcoated with a photographically sensitive coating composition by means of a reverse roll coater. The sequence in which dry components are added is not critical in preparing the coatings of the present invention. In a convenient procedure, the topcoating composition was prepared by combining, by dry weight, 0.1 part difurfurylidene pentaerythritol, 0.05 part 4-chloro-m-phenylenediamine, 0.05 part 3, S-dibromo-toluenediamine and 0.1 part iodoforrn.

To these dry components were added as a binder 6 parts (wet weight) polyphenylene oxide resin (General Electric's PFC) which was dissolved in a 10 percent chloroform solution. The entire mixture was stirred until an homogeneous composition was obtained.

This coating composition was applied to the coated substrate herein described by a reverse roll coater in an amount equal to 5 pounds per ream.

After drying, the photographically sensitive sheet thus obtained was exposed through a negative transparency using a 7.5 KVA carbon are lamp at 24 inches for 10 seconds. Development was effected by heating at 132 for seconds.

The positive image thus produced exhibited a high-optical density (Dmax of 2.0) in the image areas inverse to the colorless areas of the negative employed for exposure. Sharp, clearly defined contrast was exhibited between the nearly black image areas and the white background areas.

In a further embodiment of the practices of Example 1, a coating composition was prepared wherein difurfurylidene azine was substituted for difurfurylidene penetaerythritol, and all other components were unchanged. A clear positive image having high contrast and excellent optical density was obtained when sheets bearing this coating were exposed to a negative and developed.

EXAMPLE 2 In another illustration of the sharp photographic contrast which may be obtained by employment of the enhancer systems of the present invention, a conventionally coated and supercalendered base sheet was employed. This paper web was of bleached bodystock having a basis weight of 57 pounds per 25 inches X 38 inches-500 sheet ream. Upon both surfaces of this web a pigmented surface size containing sufficient water to make a composition of 25 percent solids had been applied by a size press in an amount equal to 3 pounds per ream per side. After drying, a second coating comprised by dry weight of parts No. 1 domestic coating clay with 10 parts starch and 5 parts styrenebutadiene latex as a binder was mixed with sufficient water to obtain 60 percent solids and was applied to one surface of the previously coated web in an amount equal to 7 pounds per ream.

The thus coated web having a basis weight of 700/ream was dried by conventional means and supercalendered through 5 nips at 1,500 pli. The web surface thus obtained was smooth enough to be desirable for photographic-quality detailed image reception.

An intermediate, continuous-film coating composition was applied in an amount equal to 40/ream, according to the method of example 1.

The thus coated web was topcoated by means of a No. 20 Mayer bar with 4 pounds per ream of a photographically sensitive coating. This coating was comprised of 0.1 pan difurfurylidene pentaerythritol, 0.02 part 4-chloro-m-phenylenediamine, 0.08 part 3,S-dibromo-toluenediamine, and 0.15 part iodoform. As in Example One, these components were mixed under vigorous agitation with 6 parts (wet weight) of a 10 percent solution of polyphenylene oxide in chloroform.

After drying of the coated sheet, exposure'was accomplished by the method of Example One. Development was by heating at 149 C. for 70 seconds.

The positive images produced upon this surface were of high-optical density in those areas inverse to the colorless portions of the negative original and exhibited excellent contrast between the near-black of the image areas and the white, unyellowed background areas.

EXAMPLE 3 While brominated amines in combination with other amines may be employed as enhancers with polyphenylene oxide resin as a binder to produce high-density photographic images of great contrast as in Examples One and Two, such contrast is not always desirable in photographic work. it is desirable for such embodiments as aerial photography to obtain high-intensity images with relatively low contrast so that minute variations in shadings may be perceived.

To obtain this result, the coated and finished basestock of Example One was topcoated in an amount equal to 6 pounds per ream by means of a No. 20 Mayer bar with a coating composition comprising, by dry weight, 01 part difurfurylidene pentaerythritol, 0.05 part 4-chloro-m-phenylenediamine, 0.05 part 3,5-dibromotoluenediamine, 0.] part iodoform, and 6 parts (wet weight) of a 10 percent solution of polystyrene (The Dow Chemical Co.-S -666U) in chloroform. The dry components were collectively added to the polystyrene solution and stirred until a homogeneous liquid was obtained.

This topcoating composition was applied in the manner of Example One and the coated sheets were dried by conventional means. I

Positive images were obtained when these coated sheets were exposed to the light source of Example One for 10 seconds, and then developed by heating at 149 C. for 80 seconds. These images were of strong intensity, but did not ex-. hibit the sharp image contrasts of sheets bearing polyphenylene oxide-bound coatings. Instead, clear distinctions could be observed between slight hue variations, and minute pictorial details were readily discernible.

In a further operation carried out according to the method of Example Three, difurfurylidene orthotolidine was substituted for difurfurylidene pentaerythritol in like amount, with all other components unchanged. When a sheet containing this furfurylidene in the topcoat was exposed and developed, intense images having low contrast and precise hue differentiation were obtained.

EXAMPLE 4 A paper web bearing the basecoatings of example 2, except that 12 parts polyvinyl alcohol were substituted for starch and latex as the binder in the second coating, was finished in the same manner as in example 2. After conventional drying and supercalendering, the thus basecoated web had a basis weight of 55 pounds per ream.

This web was topcoated by means of a No. 20 Mayer bar with a photographically sensitive coating composition prepared by combining, in the manner of example 1, 0.15 part difurfurylidene pentaerythritol, 0.] part 2,6-dibromo-l ,4- phenylenediamine, 0.1 part 3,5-dibromo-2,4-toluenediamine, and 0.15 part iodoform. all by dry weight, and mixing this combination until homogeneous in 8 parts (wet weight() of a 10 percent solution of Dows S-666U polystyrene in chloroform.

This coating composition was applied in an amount equal to pounds per ream, and the coated sheet was dried. Exposure was by a 7.5 KVA carbon arc lamp to a photographic negative at 24 inches for seconds. Development by heating in the usual manner produced intense images with medium contrast.

EXAMPLE 5 The procedures of example 4 were repeated employing a topcoating containing 0.] part difurfurylidene pentaerythritol, 0.05 part 4-chloro-m-phenylenediamine, and 0.1 part iodoform. A sheet bearing 6 pounds per ream of this coating was imaged as in example 4. The developed coated surface, which contained no brominated amine enhancer, bore images of low contrast, similar to the contrasts obtained in the images of example 4. However, the images of the unbrominated surface of the present example were markedly less intense and clear than those of Example Four.

EXAMPLE SIX The procedures of example 5 were repeated with the substitution of polyphenylene oxide for polystyrene as the binder, in like amount. Images thus produced were of low contrast but good intensity, although of a brownish color.

EXAMPLE 7 The basecoated paper of example 1 was Mayer bar coated with 5 pounds per ream of a coating composition containing 100 parts of difurfurylidene pentaerythritol, parts 2- bromo-l,4-phenylenediamine, 350 parts 3,5-dibromo-2,4- toluenediamine, 400 parts iodoform, all by dry weight, which were combined in dry form in a convenient procedure and added to a solution of 800 parts by weight of polyphenylene oxide dissolved in 12,000 parts by weight of chlorofon'n. This coating composition was stirred until homogeneous and applied to one surface of the paper. Several sheets of paper thus coated were dried and immediately imaged in the manner of example 1. Images of dark brown to black color were obtained which exhibited medium to high contrast between image areas of different hue. Others of these sheets were allowed to remain with all surfaces completely covered in a dark room at 22 C. for 6 months. At the end of this period, the sheets were exposed and developed in the usual manner. No appreciable degradation could be observed in a comparison of the sheets immediately imaged and those which were 6 months old before imaging.

EXAMPLE 8 The procedures of example 7 were followed with the amount of difurfurylidene pentaerythritol being reduced from parts to 75 parts in the coating composition. After 6 months, dark-brown to black images of medium to high contrast were obtained upon exposure and development.

EXAMPLE 9 The procedures and components of example 7 were duplicated with the substitution of 100 parts of 2-bromb-l,4- phenylenediamine and 350 parts of 3,5-dibromo-2,4- toluenediamine as enhancers and an increase to 400 parts of difurfurylidene pentaerythritol. After 6 months shelf time at room temperature in a completely darkened room, exposure and development produced dark brown to black images of medium to high contrast.

EXAMPLE l0 The procedures of example 7 were followed and the coating composition of example 9 employed with the amount of difurfurylidene pentaerythritol being reduced from 400 parts to 50 parts. lmages equal to those of example 9 were obtained after exposure and development.

EXAMPLE ll The coating composition of example 9, with the substitution of l00 parts of 4-chloro-1,3-phenylenediamine for a like amount of 2-bromo-l,4-phenylenediamine was applied by means of a No. l6. Meyer bar to one surface of a transparent plastic film (Mylar). This film was completely protected from light at normal room temperature for a period of 6 months. Upon exposure and development, dark brown to black images exhibiting medium to high contrast were obtained.

EXAMPLE 12 The coating composition of example 7, with the substitution of 100 parts of 4-chloro-1,3-phenylenediamine for 90 parts of 2-bromo-l ,4-phenylenediamine was applied to a web of flexible aluminum foil in the manner of example ll. After a 6 month storage period, as in example 11, exposure and development produced images equal to those in example 1 l.

Further representative aromatic amine enhancer systems include: 4,6-dibromo-l,3-phenylenediamine with 4,4-oxydianiline; 2-bromo-6-chloro-l,4-phenylenediamine with 3,5- dibromo-2,4-diaminochlorobenzene; 3,5-dibromo-2,4- diaminoisopropylbenzene and l,3-phenylenediamine with 2,4,6-tribromo-l ,3-phenylenediamine; 4-methoxyl ,3-phenylenediamine and 4-ethoxy-l,3-phenylenediamine with 3,5-

PREPARATION OF POLYHALO-SUBSTITUTED PHENYLENEDIAMINES The polyhalo-substituted phenylenediamines of the present invention are prepared in accordance with known procedures. The following representative operations illustrate the preparation of these compounds.

EXAMPLE 13 Preparation of 2,4-diamino-3,5-dibromo-isopropyl benzene 4isopropyl-m-phenylenediamine (30 grams; 0.2 mole) was dissolved with stirring in 100 ml. of glacial acetic acid. The stirring was continued and a solution of bromine (32 grams; 0.2 mole) in 50 ml. of glacial acetic acid was added slowly. During the of of the bromine the reaction mixture was maintained at about room temperature with an ice bath. Following the addition of the bromine the reaction mixture was diluted with water to precipitate the product as a crystalline solid. The solid 2,4-diamino-3,5-dibromo-isopropyl benzene was collected by filtration, recrystallized from chlorobenzene, and decolorized with activated charcoal. The recrystallized product was found to melt at 69.5-70.5 C.

The following polyhalo-substituted phenylenediamines em-- ployed in the present invention were prepared using this same general synthesis route: 2,4,6-tribromo-m-phenylenediamine (m.p. 153-156 C. with dec.), and 3,5-dibromo-2,4-diaminochlorobenzene (m.p. 151-l52 C.)

EXAMPLE 14 Preparation of 2,6-dibromo-1,4-phenylenediamine p-Nitroaniline was brominated by mixing together at a temperature of 90 C. a solution of p-nitroaniline (52.2 grams) in; 300 ml. of acetic acid and a solution of 128 grams of bromine in 100 ml. of acetic acid. Following the addition of the bromine, the reaction mixture was cooled, whereupon the 2,6- dibromo-4-nitroaniline intermediate precipitated as a crystalline solid. The crystals were removed by filtration and the filtrate diluted with water to induce additional crystallization of the 2,6-dibromo-4-nitroaniline.

The 2,6-dibromo-4-nitroaniline was reduced as follows: 2,6- dibromo-4-nitroaniline (60 grams) was dissolved in a mixture of calcium chloride (20 grams), zinc (80 grams). water (75 ml.) and ethanol (200 ml.). The reaction mixture was maintained at the reflux temperature for 2 hours during which time the reduction proceeded smoothly and vigorously. Following the heating period 500 ml. of ethanol was added to the hot reaction mixture, the reaction mixture brought to the boiling temperature and then filtered. Upon cooling the 2,6-dibromo- 1,4-phenylenediamine product precipitated in the reaction mixture as a crystalline solid. The solid product was separated by filtration and recrystallized from ethanol-water (55:45). The melting point of the recrystallized 2,6 -dibromo-l ,4-phenylenediamine was 138 C.

In another procedure, 2-bromo-6-chloro-1,4-phenylenediamine (m.p. 123125 C.) was synthesized utilizing the same general synthesis route.

EXAMPLE 15 Preparation of 4,6-dibromo-1 ,3-phenylenediamine The diacetate intermediate was prepared by stirring acetic anhydride (224 grams) into an aqueous solution of m-phenylenediamine (108 grams in 1,200 ml. H O). The reaction proceeded rapidly producing a crystalline solid product which precipitated in the reaction mixture. This product was separated by filtration and the solid diacetate product dissolved in 700 ml. of acetic acid and the resulting solution heated to 90 C. whereupon bromine (320 grams) was added with stirring to the heated solution. Following the addition of the bromine, the reaction mixture was diluted with water whereupon th e dibrorninated fiacetale roduct precipitated in the diluted mixture. The dibrominated diacetate product was then hydrolyzed as follows: a solution of potassium hydroxide (30 grams) in water (40 ml.) and ethanol (60 ml.)

' was warmed on the steam bath an the dibrominated diacetate (30grams added thereto. After about 10 minutes of heating crystals began to appear in the hydrolysis mixture. The mixture was then chilled in an ice bath to facilitate crystallization and filtered to remove the solid 4,6-dibromo-l ,3-phenylenediamine product which was washed, dried and found to melt at l 34135 C.

EXAMPLE 16 Preparation of 2,4-diamino-3,5-dibromotoluene Sodium acetate (50 moles, 4.0 kilo) and 2,4- toluenediamine (50 moles, 6.1 kilo) were dissolved in 35 liters of 84 percent acetic acid with stirring and cooling. When the solution reached 20 C. bromine (70 moles, 11.3 kilo) was added over a period of 45 minutes. As the temperature started to rise ice chips were added to maintain the temperature below 25 C. When the bromine addition was complete the reaction mixture was filtered immediately and the product washed well with water to yield 7.0 kilos of dark product. The 2,6-dibromo-4-methyl-m-phenylenediamine was recrystallized from acetone/water using activated charcoal to yield offwhite plates, m.p. l43.5 with violent decomposition.

The furfurylidene color-former is usually prepared by reacting furfural with a suitable amine in the case of the furfurylidene imines and with a suitable glycol or higher polyol in the case of the cyclic acetals. Conventional well understood organic synthesis techniques are used. The reaction is usually a condensation reaction carried out with an acidic catalyst in an organic solvent at temperatures in the range of to 120 C. It is preferred to use furfurylidenes in the photographic medi um that are crystalline solids at room temperature and have melting points in the range of 70 to 225 C., but liquid furfurylidenes which boil between and 220 C. at 10 mm. H, pressure can also beused. It is preferred that the furfurlidenes be soluble in CHCl to the extent of at least 0.02 gms./gm. at 25 C.

It is important to thoroughly purify the furfurylidene after its preparation in order to rid it of dark color bodies and reaction tars that would unduly tone or destroy the clarity of the background areas of the photographic medium.

We claim:

1. In a photographic plate comprising, on a support, a layer of a resinous binder containing a furfurylidene derivative color former, an amine enhancer system and a lower haloalkane sensitizer, the improved amine enhancer system consisting essentially of a mixture comprising at least one primary aromatic amine and at least one polyhalo-substituted phenylenediamine wherein the primary aromatic is selected from the group consisting of mor p-phenylenediamine, monoor di-substituted mor p-phenylenediamine, aniline, N-phenyl-pphenylenediamine, 4,4-methylenedianiline, 4,4-oxyclianiline, 4,4-thiodianiline, benzidines, or substituted benzidines and the polyhalo-substituted phenylenediamine is NE: NH:

wherein R represents bromine, chlorine, methyl, ethyl, isopropyl, R represents bromine or hydrogen and X represents chlorine or bromine; provided that when one member of mixture is 2,6-dibromo-p-phenylenediamine or 2- bromo-6-chloro-p-phenylenediamine at least one of the other members of the mixture must be a primary aromatic amine or polyhalo-substituted phenylenediamine other than 2,6- dibromo-p-phenylenediamine or 2-bromo-6chloro-p-phenylenediamine.

2. The photographic plate claimed in claim 1 wherein the furfurylidene derivative is difurfurylidene pentaerythritol. V

3. The photographic plate claimed in claim 1 wherein the resinous binder is polystyrene 4. The composition claimed in claim 1 wherein the resinous binder is polyphenylene oxide.

5. The photographic plate claimed in claim 1 wherein the furfurylidene derivative is difurfurlidene azine.

6. The photographic plate claimed in claim 1 wherein the furfurylidene derivative is difurfurylidene-o-tolidine.

7. In a photographic plate comprising, on a support, a layer of a resinous binder containing a furfurylidene derivative color-former, an amine enhancer system and a lower haloalkane sensitizer, the improved amine enhancer system consisting essentially of a mixture comprising at least one primary aromatic amine and at least one polyhalo-substituted phenylenediamine wherein the primary aromatic amine is selected from the group consisting of m-phenylenediamine, p-phenylenediamine, monohalo-m-phenylenediamines, monohalo-p-phenylenediamines, dichloro-phenylenediamines, mono-halomonomethyl-phenylenediamines, monohalomonoethylphenylenediamines, methoxy-phenylenediamines, ethoxy-phenylenediamines, 2,6-dibromop-phenylenediamine, 2-bromo-6-chloro-p-phenylenediamine, N-phenyl-p-phenylenediamine, aniline, 4,4-methylenedianiline, 4,4'-oxydianiline, 4,4-thiodianiline, benzidines, 3,3 '-dimethoxybenzidine, and 3,3 diethoxybenzidine; and

the polyhalo-substituted phenylenediamine is selected from the group consisting of phenylenediamines corresponding to either of the formulas wherein R represents bromine, chlorine, methyl, ethyl, isopropyl, R represents bromine or hydrogen and X represents chlorine or bromine; provided that when one member of the mixture is 2,6-dibromo-p-phenylenediaminc or 2-bromo-6-chloro-p-phenylenediamine, at least one of the other members of the system is a primary aromatic amine or polyhalo-substituted phenylenediamine other than 2,6- dibromo-p-phenylenediamine or 2-bromo-6-chloro-p-phenylenediamine.

8. The plate according to claim 1 wherein the polyhalo-substituted phenylenediamine is taken from the group consisting of 4,6-dibromol ,3-phenylenediamine, 2,4,6tribromol ,3- phenylenediamine, 3,S-dibromo-Z,4-diaminoisopropylbenzene, 3,5-dibromo-2,4-diaminochlorobenzene, 2-bromo- 6-chloro-l ,4-phenylenediamine, 3,5-dibromo-2,4-diaminoethylbenzene and 2,6-dibromo -l ,4-phenylenediamine.

9. The plate according to claim 1 wherein the polyhalo-sub stituted phenylenediamine corresponds to the formula 

2. The photographic plate claimed in claim 1 wherein the furfurylidene derivative is difurfurylidene pentaerythritol.
 3. The photographic plate claimed in claim 1 wherein the resinous binder is polystyrene
 4. The composition claimed in claim 1 wherein the resinous binder is polyphenylene oxide.
 5. The photographic plate claimed in claim 1 wherein the furfurylidene derivative is difurfurylidene azine.
 6. The photographic plate claimed in claim 1 wherein the furfurylidene derivative is difurfurylidene-o-tolidine.
 7. In a photographic plate comprising, on a support, a layer of a resinous binder containing a furfurylidene derivative color-former, an amine enhancer system and a lower haloalkane sensitizer, the improved amine enhancer system consisting essentially of a mixture comprising at least one primary aromatic amine and at least one polyhalo-substituted phenylenediamine wherein the primary aromatic amine is selected from the group consisting of m-phenylenediamine, p-phenylenediamine, monohalo-m-phenylenediamines, monohalo-p-phenylenediamines, dichloro-phenylenediamines, mono-halo-monomethyl-phenylenediamines, monohalo-monoethylphenylenediamines, methoxy-phenylenediamines, ethoxy-phenylenediamines, 2,6-dibromo-p-phenylenediamine, 2-bromo-6-chloro-p-phenylenediamine, N-phenyl-p-phenylenediamine, aniline, 4,4''-methylenedianiline, 4,4''-oxydianiline, 4,4''-thiodianiline, benzidines, 3,3''-dimethoxybenzidine, and 3,3''-diethoxybenzidine; and the polyhalo-substituted phenylenediamine is selected from the group consisting of phenylenediamines corresponding to either of the formulas
 8. The plate according to claim 1 wherein the polyhalo-substituted phenylenediamine is taken from the group consisting of 4,6-dIbromo-1,3-phenylenediamine, 2,4,6-tribromo-1,3-phenylenediamine, 3,5-dibromo-2,4-diaminoisopropylbenzene, 3,5-dibromo-2,4-diaminochlorobenzene, 2-bromo-6-chloro-1,4-phenylenediamine, 3,5-dibromo-2,4-diamino-ethylbenzene and 2,6-dibromo-1,4-phenylenediamine.
 9. The plate according to claim 1 wherein the polyhalo-substituted phenylenediamine corresponds to the formula 